1. FIELD OF THE INVENTION
The present invention relates to viscous fluid heaters, and more particularly, to heaters having a heating chamber and a heat exchanging chamber accommodated in a housing with viscous fluid and a rotor accommodated in the heating chamber. Heat exchange takes place between the heat generated in the heater when the rotor shears the viscous fluid and a circulating fluid flowing through the heat exchanging chamber.
2. DESCRIPTION OF THE RELATED ART
Viscous fluid heaters, which are operated by the drive force of automobile engines, have become widely used as an auxiliary heat source. Japanese Unexamined Patent Publication No. 2-246823 describes a typical viscous fluid heater incorporated in a vehicle heating apparatus.
The viscous fluid heater has a front housing and a rear housing which are coupled to each other. A heating chamber is defined in the front and rear housings while a water jacket (heat exchanging chamber) encompasses the heating chamber. A drive shaft is rotatably supported by a bearing in the front housing. A rotor is fixed to one end of the drive shaft in the heating chamber. Thus, the rotor and the drive shaft rotate integrally. Rib-like projections are provided on the front and rear surfaces of the rotor and the opposed inner walls of the heating chamber. The opposed projections are aligned with one another so as to form labyrinth grooves. Furthermore, the opposing projections are spaced from each other so as to form a labyrinth-like clearance between the outer surfaces of the rotor and the inner walls of the heating chamber. A predetermined amount of a viscous fluid, such as silicone oil, is contained in the heating chamber. The viscous fluid also fills the labyrinth-like clearance.
When the drive force of the engine is transmitted to the drive shaft, the drive shaft rotates together with the rotor in the heating chamber. The viscous fluid between the inner walls of the heating chamber and the outer surfaces of the rotor are sheared by the rotation of the rotor. This results in fluid friction and produces heat. Heat exchange occurs between the heating chamber and the coolant circulating through the water jacket. The heated coolant is then sent to an external heater circuit to warm the passenger compartment.
The prior art viscous fluid heater described above requires the rib-like projections to be formed on the front and rear surfaces of the rotor to form the labyrinth grooves. Accordingly, a rotor body is disk-like and the axial length of the body is shorter than the radius of the body. In such a rotor, the main shearing surface corresponds to the rib-like surfaces provided on the front and rear surfaces of the rotor. Furthermore, the rotating speed (i.e., shearing speed) of the rib-like projections becomes higher at positions located farther from the axis of the rotor body. Thus, it is necessary to enlarge the rotor diameter, that is, the outer diameter of the rotor body, to increase the heating value of the heater. However, space, and especially, space in the engine compartment, is limited. Thus, if the radius of the viscous fluid heater is large, it is difficult to provide sufficient space for the heater in the engine compartment. Furthermore, a large viscous fluid heater affects the layout of other equipment in the vehicle.